1. Field of the Invention
This invention relates to a novel chemically modified vegetable oil-based industrial fluid having superior performance properties and to methods for its preparation.
2. Description of the Prior Art
Most of the lubricants currently in daily use originate from petroleum base stocks that are toxic to environment, making it increasingly difficult for safe and easy disposal. There has been a increasing demand for “green”lubricants [Rhee, I., NLGI Spokesman, 60(5):28 (1996)] in recent years due to concerns about loss of mineral oil-based lubricants to the environment and increasingly strict government regulations controlling their use. Losses from accidental spillage and non-recoverable usage can result in ground water contamination and pose a threat to animal and plant life.
Vegetable oils such as rapeseed oil and high oleic varieties of other oils are considered to be potential candidates to replace conventional mineral oil-based lubricating oils and synthetic esters [Randles, S. J. et al.; J. Syn. Lubr., 9:145 1992); Asadauskas, S. et al.; Lub. Eng., 52:877 (1996)]. Vegetable oils are non-toxic, renewable resources and lower cost alternatives to synthetic fluids. The primary industrial application of vegetable oil use has been in the area of biodegradable hydraulic fluids. They have very low volatility due to high molecular weight of triacylglycerol molecule and narrow range of viscosity change with temperature. The ester linkages deliver inherent lubricity and enable the oils to adhere to metal surfaces. Further, vegetable oils have higher solubilizing capacity for contaminants and additives than mineral base fluids.
The most serious disadvantage of vegetable oils is their poor oxidative stability [Becker, R. et al.; Lubr. Sci., 8:95 (1996); Gapinski, R. E. et al.; SAE Tech Pap. 941785, pages 1-9 (1994)], primarily due to the presence, of bis allylic protons. These protons arc highly susceptible to radical attack and subsequently undergo oxidative degradation to form polar oxy compounds. This oxy-polymerization process ultimately results in insoluble deposit formation, and an increase in oil acidity and viscosity. Vegetable oils also show poor corrosion protection [Ohkawa, S. A. et al.; SAE Tech paper 951038, pages 55-63 (1995)], and the presence of ester functionality render these oils susceptible to hydrolytic breakdown [Rodes, B. N., et al.; SAE Tech paper 952073, pages 1-4 (1995)]. Therefore contamination with water in the form of emulsion must be prevented at every stage. Low temperature studies have also shown that most vegetable oils undergo cloudiness, precipitation, poor flow and solidification at cold temperatures.